European Union leaders will on Monday back closing down the Balkans route used by most migrants to reach Europe, diplomats said, after at least 25 more people drowned trying to cross the Aegean Sea en route to Greece.

The declaration drafted by EU ambassadors Sunday will be announced at a summit in Brussels on Monday, set to also be attended by Turkish Prime Minister Ahmet Davutoglu.

The bloc's 28 leaders will ask Davutoglu's government to accept "large-scale" deportations of economic migrants from Greece, the main entry point to Europe, and do more to implement a November deal to slow the flow of people into the bloc.

Greece has seen non-EU Macedonia and EU countries on the western Balkans route virtually shut their borders in a domino effect, trapping Syrian and other asylum seekers desperate to head north to wealthy Germany and Scandinavia.

An EU diplomat told journalists that European leaders would declare Monday they will "close the Balkans route in the coming days," ending the "wave-through approach" to migrants that has caused chaos and tension in Europe.

Another diplomat confirmed that the language contained in an earlier draft declaration remained: "Irregular flows of migrants along the western Balkans route are coming to an end".

The diplomat cautioned that delegations were still looking at the draft, as is always the case before a summit.

Help for Greece

Brussels on Friday unveiled a plan to restore by the end of the year the full functioning of Europe's cherished passport-free Schengen zone after the series of border closures.

It was timed with calls for not only better cooperation from Turkey but also the creation of an EU coastguard force by the summer and help for Greece to strengthen its external border.

EU leaders are set to stand by Greece after having last week promised 700 million euros in emergency aid for the country and other states to help them manage the influx at their borders.

Greek Prime Minister Alexis Tsipras on Sunday demanded the "urgent" relocation of thousands of refugees to other member states.

The bloc adopted a scheme last September to relocate 160,000 asylum seekers from Greece and Italy, but fewer than 700 people have actually been moved.

Donald Tusk, the European Council president and summit host, said in his invitation letter that success depended largely on securing Turkey's agreement for the "large-scale" readmission from Greece of economic migrants who do not qualify as refugees.

Syrians, who top the influx of people into Europe, are considered genuine refugees requiring admission under international law.

Davutoglu told reporters at Istanbul airport before leaving for Brussels that Turkey had taken "important steps" to fulfil its part of the stalled November deal.

He said there had been a drop in numbers, but "not a dramatic decline" because of the ongoing civil war in neighbouring Syria.

Despite progress, the EU said too many people were still heading from Turkey to Greece, with nearly 2,000 arriving daily in February.

The Financial Times reported Sunday that Brussels had drafted a proposal to centralise the system for processing asylum applications, removing the current rule that requires asylum seekers to lodge their claim in the first EU country they arrive in.

The proposal is part of a radical overhaul of its refugee policy to be announced at a summit on March 17.

25 migrants drown

Just ahead of the Brussels meeting at least 25 migrants, including ten children, died after their wooden boat capsized trying to reach Greece, the Turkish coastguard said. Fifteen people were rescued off the Turkish coastal town of Didim Sunday.

Turkey is the launch pad for most of the more than one million refugees and migrants who have come to the continent since early 2015.

Davutoglu said he would discuss with his EU counterparts efforts to start within weeks building schools and hospitals for refugees with the three billion euros ($3.3 billion) pledged by Europe under the November deal.

Outspoken Czech President Milos Zeman said the EU should not give Turkey the funds because it was "neither ready nor capable" of helping migrants. "It's only wasted money," Zeman told TV Prima.

NATO Secretary General Jens Stoltenberg said meanwhile the alliance was broadening its new mission in the Aegean Sea to stop migrant smugglers while working more closely with the EU border agency Frontex.

British Prime Minister David Cameron announced Sunday that the Royal Navy was sending vessels to join ships from Canada, Germany, Greece and Turkey already deployed.

The International Organization for Migration said before Sunday's deaths that a total of 418 people had died or gone missing already in 2016, most while attempting to reach Greece from Turkey aboard unseaworthy boats.